Cruise the hallways of Microsoft's Redmond campus, peer into doorways, and observe what kinds of collaborative apps are running on the multiple monitors attached to every PC.

Here are some you won't often see: Yammer, SharePoint, Skype, and the Web versions of Word, Excel, Outlook, and PowerPoint. On a developer's machine you'll always see Visual Studio. On a product or program manager's machine you might see Word, Excel, or PowerPoint.

But there's one app you'll always see. It dominates all others, it runs everywhere, it's the first app you install on a fresh PC, and it's the one you'll call support in the middle of the night to fix. It's deeply wired into the company's DNA, and it remains, as it has always been, the bedrock of online collaboration at Microsoft.

What is this 800-pound-gorilla app? As you've already guessed, it's Outlook.

It embodies a way of working together that predates the dawn of the Internet and has changed very little since. Outlook users collaborate by sending email to one another, often with attachments that are edited and sent back. That seemed revolutionary 30 years ago. But even then it wasn't.

On our local area networks we re-created a way of working that enshrined what earlier generations of office workers did. They moved documents from desktop to desktop, back when documents were paper and desktops were formica. If you only make the documents electronic and the desktops into screens, you miss what's truly revolutionary about electronic networks: the opportunity to work together in shared online spaces.

I joined Microsoft during Ray Ozzie's tenure. I hoped he would change the place in two ways: shift the focus to the cloud, and modernize its collaborative tools and mind-set. One out of two ain't bad! He kickstarted Microsoft's cloud infrastructure, and while Azure was late to the game, it has matured nicely, it continues to evolve in the right ways, and it is a powerful competitor in its rarefied category.

Things went nowhere on the collaboration front, however. Never mind that Ozzie is one of the world's top experts in what he has often called CSCW (computer-supported collaborative work). Or that he was the driving force behind Lotus Notes. Or that he went on to create a next-gen product, Groove, that focused explicitly on the idea of working in shared online spaces. When he arrived at Microsoft the antibodies rejected Groove, part of which ended up deep in the bowels of SharePoint. Outlook, with its antiquated model of office work, prevailed.

What exactly is a shared online space? A great modern example is Slack. When users of Slack send messages and exchange documents, they do so primarily in the context of channels. A channel is a shared online space. Whether frequented by members of a team, by everyone in a company, or by an even wider public, messages in a channel do not begin with a decision about whom to include on a to: or cc: line, and thus implicitly whom to exclude. Things are public by default within the scope of the channel's membership. That encourages spontaneity, enhances peripheral awareness, and invites serendipity.

Some say there's nothing all that special about Slack's implementation of shared spaces -- I tend to agree. The social networks we enjoy with our friends and families showed us what's possible, and they prepared us for business networks that deliver the same spontaneity, peripheral awareness, and serendipity. Slack's timing was perfect. The business world was ready to embrace it.

At an offsite meeting someone once joked that one way to reform Outlook culture would be to make all email transparent and company-public by default. Of course there are reasons why that could not and should not happen.

Invite people to find other ways to collaborate -- for an hour a day, or a day a week -- using the many other tools available. Reward them for finding innovative ways to use Office 365's shared spaces: Yammer groups, Skype team chats, SharePoint blogs and wikis, the Web versions of the Office apps. Convert that learning into a collaboration suite that helps accelerate its own improvement and adds up to more than the sum of its parts. That's something the world needs, is ready for, and will buy.